The Personal Defence Weapon 
PDW  is a relatively new term for an old class of weapon: the self-defence gun
for troops whose duties do not involve carrying rifles.

Thisis a separate issue from the carrying by infantry of pistols as supplementary weapons,a practice which has increased in
those armies which were
engaged in Iraq and Afghanistan mainly to ensure that troops are
always armed due to the risk of close-range attack by
insurgent infiltrators even within supposedly safe bases. For example,
the British Army largely ignored pistols throughout the Cold War era,
but in 2013 decided to replace all of its old Browning P-35s with Glock
17 pistols selected mainly because of their fast handling, and
introduced training in their rapid use. This
is significant change from the past when in most armies (the US being a
notable exception), handguns were often regarded as more of a hazard
than an asset as they were a common source of NDs (negligent
discharges)
and allegedly wereresponsible for more friendly than
enemy casualties. Better training should help with this, of course, but even so the practical range in the hands of
non-specialists is extremely short, especially in the stress of
combat.

The
case for the PDW is to address circumstances in which a firearm much
lighter
and more compact than a rifle, but more effective over a longer range
than a pistol, is desirable. Examples of potential users include vehicle crews, since the interiors of
AFVs and attack helicopters tend to be rather cramped, and troops primarily operating other weapons, such as MANPADS,
or for those on police or protection duties.

With admirable foresight, the
US Army recognised this need and introduced the self-loading .30 M1 Carbine
in 1942, primarily as a handgun replacement. Chambered for a much smaller and
less powerful 7.62 x 33 cartridge than the .30 M1 (Garand) rifle, the Carbine was a light
and handy weapon which saw service in more offensive roles than were originally
intended, particularly in the M2 version which introduced a selective fire
capability.

Other armies seeking to improve
effectiveness turned to the sub-machine gun firing pistol ammunition (SMG). Introduced
in the First World War, they were commonly carried by NCOs in the Second, as
well as specialist troops and  in the case of the Soviet Army  whole regiments
of infantry. The support gained from firing from the shoulder gives these a far
longer effective range than a pistol; around 100 metres or so. They are also
more compact and handier than rifles but not usually any lighter, and in
practice have been used more for offensive than self-defence roles. There have been some post-WW2 exceptions in the form of particularly light and compact SMGs, most notably the Polish PM-63 RAK, which
weighs only 1.6 kg empty but only fires the 9 x 18 Makarov round, less
powerful than the standard Western 9 x 19. Another example, also from the early 1960s, is the CzechoslovakianSA vz 61 Scorpion, but
this is chambered in the even weaker 7.65 x 17SR (.32 ACP) round, which
is not generally considered to be powerful enough for military
purposes. It did allow the empty weight to be reduced to only 1.28 kg.
These may both be considered as PDWs, designed and employed primarily
for defensive purposes. Another SMG based on a low-powered cartridge,
which was not successful, was the compact MAC 11, chambered for a heavy
loading of the 9 x 17 (.380 Auto) pistol round.
In the last
quarter of the 20th Century, SMGs were gradually replaced in many
armies by shortened versions of the standard rifles, which in the new small
calibres (5.56 x 45 and 5.45 x 39) are just as compact as most conventional SMGs, usually lighter, and
have the benefit of simplifying training and logistics. As a result, the most common
combination of compact weapons in most armies now consists of a short carbine and a
handgun. The US Army, for instances, relies primarily on the 5.56 mm M4 Carbine
and the 9 mm M9 pistol. Despite
this, there is a body of opinion that neither weapon is entirely
satisfactory in the PDW role: the pistol for reasons already given, the
carbines because they use ammunition designed to give optimum
performance in long barrels of around 500mm. Even with short barrels,
the carbines are generally bigger and heavier (3 kg) than a PDW should
be, and the increased muzzle flash and blast resulting from their short
barrels does not help in training non-infantry troops to shoot
accurately; already a problem given the limited small-arms training
they usually receive.

Body
armour, the NATO response and terminal effectiveness

Another factor which has come
into play concerns the development of body armour using modern synthetic
materials; a weapon unable to penetrate the more commonly-found levels of armour
is likely to prove of increasingly limited value. NATO recognised this problem
and in 1990 commenced the task of defining the characteristics of the ammunition
required to replace the NATO standard 9 x 19 pistol / SMG round. The key to this
was the ability to penetrate a specified level of body armour (named the CRISAT
target for the Collaborative Research Into Small Arms Technology project),
defined as a 1.6 mm titanium plate and 20 layers of Kevlar, while retaining
sufficient energy to incapacitate the man wearing the armour, out to a range of
150 metres. Two different weapons were envisaged for this ammunition; a
short-range (50 m) PDW weighing less than 1 kg (effectively a pistol) and a
medium-range (150 m) close defence weapon weighing less than 3 kg (a compact SMG). Curiously, the PDW tag has since become transferred to the close defence weapon.

The first contender was FNs 5.7
x 28 round, as chambered in the compact P90 SMG and subsequently the Five-seveN
pistol. This penetrates the CRISAT target by means of its small calibre
and high velocity (a 2.0 g bullet is fired at 715 m/s from
the P90, for a muzzle energy of 511 J). The ammunition is lighter and slimmer than the 9 x 19,
allowing the pistol magazine to hold 20 rounds, and the P90 to carry 50. Recoil is also lighter than
either the 9 mm or the 5.56 mm, making the weapons easier to shoot accurately.

At first, it seemed that NATO
standardisation for the FN ammunition would follow without opposition, until
Heckler & Koch introduced the 4.6 x 30 cartridge at the end of the 1990s,
initially available in the MP7 machine pistol (with the P46 pistol intended to follow).
The performance as currently loaded matches the 5.7 mm (a
2.0 g bullet fired at 720 m/s
for 520 J) with the smaller calibre helping with penetration and energy
retention. Various trials were held between 2000 and 2003 and, while both rounds
met the requirements, the FN cartridge generally came out ahead
(the performance of the 4.6 mm has been increased since
then).
However, the necessary consensus between NATO countries proved impossible to
achieve so no standardisation has taken place: it is left to each country to
make its own choice.

In
2008 NATO announced its intention to replace the CRISAT armour
specification with two new standards, for soft and hard (ceramic)
armour, to reflect technical developments. The implications of this for
ammunition performance requirements is not yet clear, but the strongest
hard-plate armour can now resist all but armour-piercing rifle
ammunition, so it will clearly be very difficult for any smaller and
less powerful weapon to be effective against it.

A
disadvantage of the small calibre / high velocity route is often argued
to be the lack of terminal effectiveness in soft tissue. There is no
escaping the fact that the 5.7 mm and 4.6 mm rounds are smaller and
less powerful than the 5.56 x 45, which has itself been criticised for
lack of effectiveness, and produce smaller wound channels in ballistic
testing. However, the true comparator should be the 9 x 19
military ball loading, which the PDW rounds are intended to replace.
Proponents of the small calibre rounds point to the fact that unlike
conventional pistol ammunition their pointed bullets lose stability and
turn over on impact, creating a much larger wound channel than
the small calibre would suggest. Some anecdotal accounts of the use of
the P90 in action support this, while others (especially from US police
sources) report a worrying lack of effectiveness. This seems to
parallel experience with the 5.56 x 45; small-calibre high-velocity
(SCHV) bullets sometimes work spectacularly well but on other occasions
fail badly, depending on exactly where the bullet strikes and how it
performs thereafter. Large calibre bullets tend to have a more
consistent effect.

The ideal
would of course be to combine effectiveness against both protected and
unprotected targets. Some point out that the West's current opponents do
not usually wear body armour, but it would be very short-sighted to assume that
this will continue to be the case. As noted above, no cartridge in the PDW
class can hope to penetrate the kind of body armour currently being worn by
Western military forces so some argue that it is best to forget about AP ability
and concentrate on soft target effectiveness, relying on headshots to deal with
armoured targets. But there are, of course, various classes of body armour, and
insurgents may not choose to wear the very bulky and heavy hard-plate military issue.
Furthermore, if well-armoured opponents became the rule this would
shift the balance of advantage back to the SCHV route, as the flat trajectory,
light recoil and large magazine capacity of 5.7 mm or 4.6 mm weapons would
increase the probability of achieving a headshot.

The Russian and Chinese approach

Perhaps the most interesting
recent development has been the Russian adoption of the 9 x 19 round, just as NATO was
searching for its replacement. In this case, the 9 x 19 is seen as usefully
more effective than the long-established 9 x 18 Makarov (an attempt to boost the
performance of the Makarov round up to NATO 9 x 19 levels with the 7N16
high-pressure loading was abandoned because of the danger of using this in older
guns). The effectiveness of the new Russian 9 x 19 is
significantly enhanced by the development of new loadings which combine the
ability to pierce body armour with the benefits of a full-calibre bullet against
unprotected personnel. It achieves this by means of a method of construction
which is similar to that of Second World War APCR, HVAP and PzGr 40 anti-tank
gun projectiles: the bullet has a hard sub-calibre core contained within an
outer sleeve and separated from it by a polyethylene layer.

If the bullet strikes an unarmoured target, it holds together to produce a wide wound channel.
On impact with armour, the sleeve is stripped away and the core penetrates
alone. Two different loadings have been introduced: the 7N21 (5.3 g at 460 m/s
for 560 J muzzle energy) and the 7N31 (4.2 g at 600 m/s for 756 J -
both figures are from pistol barrels). The latter
in particular is a very high-pressure loading which can only be used in
particularly strong pistols. Not satisfied with improving the 9 x 19 in this
way, the Russians have also introduced a longer 9 x 21 round for special
forces weapons to achieve the same effect. The 7N29 AP loading fires a 6.7 g
bullet at 410 m/s for 560 J, and will reportedly penetrate two 1.2 mm
titanium plates plus 30 layers of Kevlar at 50 m. This
Russian approach appears to provide the best of both worlds. The
disadvantage is that high impact velocity is needed for this to work, so the
bullets (especially in the 9 x 19) are relatively light to maximise the
muzzle velocity. This does mean that they will lose velocity relatively
quickly, limiting their effective range in SMGs.

Russian 9mm
composite AP bullet, showing the penetrating core and the remains of the
sleeve after hitting armour

Mention
should be made of the Russian 5.45 x 18 round developed for the very
compact PSM pistol and experimentally tried in an SMG. This would seem
to meet the criteria for a PDW but is in fact far too weak and
ineffective for the role, developing only 128 J muzzle energy from a
pistol barrel.

The Chinese have also recently
adopted the 9 x 19 round in a DAP-92 steel-cored loading (8 g at 400-430 m/s,
for 640-740 J). This appears to be primarily for police use, however: the
military are adopting a steel-cored 5.8 x 21 which is a little less powerful
than the FN 5.7 or the HK 4.6 mm rounds: it fires a 3.0 g bullet at 530 m/s for
a muzzle energy of 420 J (from an SMG barrel). Both of these rounds are used in pistols and SMGs, and
are credited with penetrating a 1.3
mm 232 helmet steel plate, plus 50 mm of pine wood block behind it, at up to 100
m range.

The USA - PDW, or a return to the .45?

Mixed signals are emerging from the USA. Experience with the 9 mm M9
pistol in Iraq has led some in the US Army to regard this calibre as
unsatisfactory in terminal effectiveness (the military being limited to
using full metal jacket rounds rather than the considerably more
effective expanding bullets commonly used by police forces). However,
the likely direction of any change is hard to fathom. US forces have always kept some .45 pistols in service, most
recently the H&K MK23 selected in the mid-1990s for offensive use
by Special Forces, and in 2006 there was
considerable interest in selecting a new pistol in this
calibre. Comparative trials with a variety of pistols
chambered in 9 mm, .40 S&W and .45 ACP were carried out, and the USSOCOM (Special Operations
Command) subsequently announced that it intended to issue a solicitation to
obtain a commercially available non-developmental item (NDI) Joint Combat Pistol
(JCP) system, Calibre .45 (ACP). There was to have been an initial order for 24
Engineering Test Units (ETU's), but the maximum quantity expected to be acquired
was more than 600,000 pistols: enough to replace the 9 mm pistols altogether.
In the event, SOCOM cancelled its plans in September 2006.

Only a couple
of months later, the USAF announced its intention to acquire a new pistol,
probably in either .40 S&W or (preferably) .45 ACP calibre. This plan too was
put on hold in 2007. The US Coast Guard has recently changed to the .40 S&W
calibre.

The
US has of course had a strong emotional attachment to the .45 ACP
calibre since its adoption almost a century ago, but this new interest
was surprising as the cartridge has little ability to penetrate even
the most basic body armour.

In
contrast, the USMC did acquire a dozen each of the P90 and MP7 in the
early 2000s for evaluation, but no results ever emerged. However,
it was reported in March 2007 that the US Army is looking to acquire a
new PDW. The head of the Army's "Program Executive Office - Soldier"
stated that a formal requirement for a PDW which would be "larger than
a pistol and smaller than a carbine" was being drawn up at the Fort
Benning infantry centre, and that the Army's small-arms development
centre at Picatinny Arsenal would be in charge of overseeing the
procurement. No further information was released concerning the calibre or type of weapon, or whether an
off-the-shelf buy or a new development would be favoured. Given the
recent track record of several recent US attempts to acquire new small
arms, some scepticism as to whether this would lead to anything was in order;indeed, by 2012 there was still only a vague mention of the possibility in Army briefings. The
most recent (2013) information is that a modular, multi-calibre
(presumably 9 x 19, .40 S&W and .45 Auto) pistol design is to be
pursued for US forcesin the medium term.

Various
new cartridges in the PDW class have been developed, so far without
military adoption. Most have taken the form of small-calibre rounds
which fall into one of two groups: those intended to fit within pistol
handgrips, and longer and more powerful ones for use in
purpose-designed compact carbines. The latter group clearly cannot meet the NATO PDW requirement as they are unsuitable for use in
pistols; they are purely carbine rounds, and really the spiritual successor to
the .30 M1 Carbine cartridge.

The first of the longer rounds was the .22 APG Carbine (Aberdeen
Proving Ground) of the 1950s, designed to use the action of the .30
Carbine then in service. The 5.56 x 33 case was not based on the .30
Carbine necked down as might be expected, but on a wider case the
same diameter as that of the 5.56 x 45. A very similar round is
the commercial .221 Remington Fireball (5.56 x 34), designed for a
specialist civilian bolt-action pistol but also adopted in the late
1960s for the prototype of the IMP-221 USAF survival weapon, which was
a stockless bullpup - a concept later adopted for the commercial
Bushmaster "arm pistol". Two other very similar cartridges emerged, the
Colt 5.56 x 30 MARS of the 1990s and the Indian 5.56 x 30 MINSAS from the late
2000s. A variation on this theme is the 6
x 35 cartridge from Knight's Armament Company in the USA. This is made
by slightly necking-out as well as shortening the 5.56 x 45 case to
take a 4.2 g bullet which achieves 740 m/s when fired from a 254 mm
barrel, developing a muzzle energy of 1,150 J. It is claimed to
slightly exceed the muzzle energy of the 5.56 x 45 when both are fired
from 254 mm barrels, while producing considerably less flash, blast and
recoil, and to be effective out to 300 m. While KAC PDW is still
advertised and might make a useful supplementary weapon to those few
armies whose standard infantry rifle uses the full-power 7.62 x 51
round, it is hard to imagine that any army using 5.56 x 45 weapons
would want to add a calibre which is so close in performance to the
5.56mm. One other carbine-only cartridge which is still advertised is
the Czech .17 Libra (4.38 x 30) based on a much slimmer cartridge case.

The pistol-compatible group of small-calibre experimental cartridges
kicks off with the Colt .22 SCAMP of the late 1960s, which like the IMP
described above was originally intended to meet a USAF requirement
for a survival gun. The cartridge was a 5.56 x 29, based on a much
slimmer case than the 5.56 x 45, and intended to be burst-fired from a
large pistol. Also based on slimmer cases were the 5.7mm GIAT (5.7 x
22), which was dropped in favour of the FN P90 when GIAT acquired the
company, the Belgian 7.9 x 24 VBR and the Italian 7mm Penna range. In
contrast, the .224 Boz (5.56 x 23) was based on the wider case of the
10mm Auto cartridge and thereby generated 718 Joules. Even wider is the
case for the JAWS Micro-Mag range (developed in the USA for Jordan),
which is based on the .45 Auto case
necked down in various calibres, including .225 (5.56 x 25) and .250
(6.35 x 25). The remainder of the rounds described here all share more
or less the same case diameter as the 5.56 x 45, the 9 x19 and the
obsolescent 7.62 x 25 Tokarev (they differ structurally mainly in that
the
base of the 5.56mm case is much stronger to cope with the higher
operating pressures). These include the Czech .224 VA (5.56 x 23) and
the .22 TCM (5.56 x 26), a commercial pistol round from Rock Island
Armory. The final pair are unusual in that they utilise saboted
ammunition: the .223 Timbs, which is simply the 7.62 x 25 Tokarev case
loaded (to a very high pressure) with a saboted 5.56mm commercial
bullet, and the
6.5 x 25 CBJ, about which more below. It will be noticed in the photo
below that not all of these rounds are short enough to fit into actions
designed for 9 x 19; the SCAMP, the JAWS rounds, the .22 TCM and .223
Timbs all require longer actions, e.g. long enough for the 7.62 x 25
Tokarev or the .45 Auto.

The diagram below shows the
calculated recoil energy factors for typical loadings of various PDW cartridges.
When fired in guns which are of similar weight and design, the recoil energy
developed by the gun will be proportionate to these factors.

The 6.5 x 25 CBJ

An alternative approach
to the PDW has been
developed by CBJ Tech of Sweden: the 6.5 x
25 CBJ cartridge. The cartridge has the same overall dimensions as the 9 x 19,
and 9 mm guns can fire the 6.5 mm round with just a change of barrel (they can
use the same magazines). The standard ball round fires a saboted tungsten 4.0 mm
diameter sub-projectile at high velocity: 2.0 g at a muzzle velocity
varying between 730 and 900 m/s depending on barrel length, with the lower
figure from a 120 mm barrel (giving muzzle energies varying between 533 and 810
J), thereby achieving
good armour penetration out to a claimed 400 metres from the longest (300 mm)
barrel. Other sub-calibre and full-calibre loadings have also been developed.

CBJ also designed their own gun to fire this ammunition, the CBJ MS (a compact
SMG with a clip-on bipod) and at the time
of the NATO trials this received marketing support from SAAB-Bofors, but this
company is no longer involved. The
parent company continues to develop the ammunition and is in discussion with possible manufacturers;
the focus now is in adapting existing pistols and SMGs rather than pushing the
MS.

In mid-2009 the author was
contacted by Mr Johansson, the founder of CBJ Tech, who had read an earlier
version of this article and been inspired to get together with Brugger & Thomet
to produce a version of the MP9 in 6.5mm CBJ. The prototype was being tested and
I was invited to Sweden to see it for myself. This combination was still in the
development phase (complicated by a recent change in the cartridge case which
affected its capacity) so some fine-tuning was still required. Even so, the
potential was evident, as I found when I had the opportunity to try the
gun in both 9mm and 6.5mm versions, in semi-automatic and automatic fire.

The MP9 is
one of those guns which just feels "right" to hold and shoulder. It comes
naturally into the aim, and is very comfortable to shoot as well as surprisingly
controllable for such a light weapon. Even in 9mm, short bursts could be grouped
closely enough to keep the rounds on target out to perhaps 20-25 metres. The
6.5mm version was even better, as recoil felt slightly lighter. The 6.5 mm's high muzzle
velocity of around 800 m/s provides a flat
trajectory, giving a realistic effective range of about 200 metres in semi-auto
fire. I witnessed armour-piercing and gel tests of the CBJ ammunition, the
latter being compared with 9mm ball as shown below. I came away with my view of
the potential of this gun and ammunition combination very much confirmed. My
only complaint was that I couldn't take the little gun home with me...

More information on CBJ ammunition is
available from their website HERE.

Top: some views of the 6.5mm MP9 above, fitted with
a 1.5x Trijicon ACOG sight (note the cartridge case in mid-air).

Above: three of the CBJ cartridges shown next to a 9
x 19 for comparison: sub-calibre tungsten ball round; full-calibre
frangible; full-calibre High Energy Transfer (HET)

6.5mm CBJ results:

Left, penetration of 9mm thick armour plate from a
Russian armoured vehicle by the standard saboted tungsten ball round,
achieved from a 300mm barrel (900 m/s). The diameter of the hole is about
6mm. The 5.56mm SS109 steel-tipped ball caused a shallow gouge, the 7.62mm
lead-cored ball just left a splash mark.

The choice of guns is of
course intimately tied to the choice of calibre. One possibility is to retain
the current common practice of issuing a 5.56 x 45 carbine; in fact, the USMC announced in summer 2007
that in future almost all officers going into combat would be issued with the M4
rather than the M9 pistol. While much more effective than any pistol, the M4 is
clearly not an ideal solution: a PDW should be small enough to be carried on the
person without it being a burden or interfering with the soldier's primary task,
or alternatively be easily stowable in (and deployable from) a vehicle turret or
aircraft cockpit. The M4, although fairly light,
is 838 mm long when ready for use (757 mm with butt collapsed) despite its
short, 370 mm barrel.

To some extent, the M4's
problems could be addressed by adopting a much more compact 5.56 mm weapon:
which means a bullpup. One already in service is the British Army's L22A2, a
short-barrelled version of the SA80 intended for AFV and helo crews. This is
certainly short at only about 555 mm overall, but it is
heavy and in any case is not available for anyone else to purchase: the last
SA80s were made some 20 years ago and the L22s were adapted from existing
weapons.

The author trying out the
L22A2. It was very comfortable to shoot, the weight making the recoil
negligible and the forward handgrip being a definite plus. However, I might
not have enjoyed it without the ear defenders...The 4x SUSAT is
inappropriate for the use this gun is designed for (as well as adding too
much weight and bulk), a 1x holographic red dot sight would be much better.

One modern bullpup which is
certainly available is theIsraeli IWI Tavor. The most compact version is
the Tavor
X95
(550 mm long with a 330 mm barrel, and 2.98 kg) which is available in either
5.56 x 45 or 9 x 19. Another is the Steyr AUG, available
with barrels of 350 mm or 407 mm, with overall lengths of 647 and 704 mm
respectively, and weights of around 3.5 kg. However, although quite short, all
of these 5.56 mm bullpups are rather bulky.

Earlier in 2007 a
private US company, MagPul, announced its PDR (Personal Defence Rifle),
a remarkably small bullpup at just 457-508 mm long with a 267-317 mm
barrel, and a projected weight of not more than 1.8 kg. Further information isHERE. Unfortunately, this interesting development has so far been taken no further.

The disadvantages of
short-barrelled 5.56 x 45 guns in terms of excessive power bringing considerable
muzzle flash, blast and recoil, have already been mentioned, and clearly the
shorter the barrel and the lighter the gun the worse these will be. Short
barrels also significantly reduce the terminal effectiveness of the SS109 / M855
bullet. These considerations led to the development of the KAC PDW in their new
calibre of 6 x 35. It weighs 1.8 to 2.3 kg depending on barrel length (20 cm or
25 cm), and with a 20 cm barrel the gun measures 660 mm with stock extended, 440
mm folded. This is a handy and efficient carbine but, as mentioned in the
ammunition section above, the cartridge is probably too close in performance to
the 5.56 x 45 for an army to want both.

The pistol-calibre PDWs

This takes us to the
PDWs designed to use the same cartridges as the service pistols, which must
therefore be short enough to fit into a handgrip magazine, as well as
ballistically suited to very short barrels. Ammunition currently in service in
this category is therefore the 9 x 19 (NATO or Russian), 9 x 21 (Russian), 5.7 x
28 FN, 4.6 x 30 HK, and 5.8 x 21 Chinese. Some older
weapons in the obsolescent Russian (now Chinese) 7.62 x 25 Tokarev pistol/SMG
calibre are also still around.Traditional SMGs
are heavy due to their use of a simple blowback mechanism which requires a
massive bolt, but many of the new generation use locked-breech mechanisms, making them
much lighter and more compact.

Examples
of current weapons are given below. They all have folding or telescoping stocks
except for the FN P90 and Chinese Type 05, which are bullpups.

In 2008 the author had the opportunity
to fire several pistol-calibre PDWs, as shown on the right (from top to
bottom): 9mm HK MP5K (folding stock), 9mm Steyr TMP (the precursor to the
B&T MP9), 4.6mm HK MP7 (stock collapsed) and 5.7mm FN P90. Unfortunately,
range restrictions meant that only semi-auto fire could be used, but the
results were still of interest.

The MP5K is the
only gun with a traditional SMG layout, but it was the most comfortable to
shoot and had no more perceived recoil than the 4.6mm and 5.7mm guns.

The Steyr TMP had no shoulder stock, which drastically
reduced its accuracy even on single-shot; it would have been an
uncontrollable bullet-spray on auto.

The MP7 was comfortable to shoot, but needed an
optical sight.

The P90 was less comfortable than the other stocked
guns: the position of the forward handgrip is much less intuitive than the
others, and the hands are very close together. The optical sight also has a
faint T-shaped aiming mark rather than the brighter red dot which I
prefer.

The photos below show the different weapons in the
aim: notice the varying elbow angles, and how cramped the P90 position is.

Below left: Steyr TMP. Below right: MP5K

Bottom left: MP7. Bottom right: P90

The B&T MP9
(top) compared with the HK MP7, to scale (both are fitted with Eotech
holographic sights).

Note that the
MP9's stock folds rather than telescoping, with the butt lying alongside the
foregrip. The MP9's foregrip is fixed (although a folding one has been
developed) while the MP7's folds backwards.

Conclusions

There is
clearly no agreement on any aspect of the choice of PDW; not the type of
cartridge, nor
the type of weapon. There are no "right answers", just a range of
options with different pros and cons. Selection also has to be considered as
part of the "suite" of weapons and ammunition available in any particular army. So this author,
observing from the sidelines, is sticking his neck out in
making any suggestions. However, here goes...what follows is my own armchair
(or, at best, shooting bench) opinion.

Pistols do not make
effective PDWs except for very close-range emergencies; they are simply too inaccurate in all but highly-trained hands,
especially in the stress of combat. To achieve even a passable hit probability, a PDW should have a shoulder stock and
preferably a fore-grip; a combination
which dramatically improves its usefulness over any pistol. An automatic
fire option improves the effectiveness of suppressive fire, a useful facility in
keeping down the heads of ambushers when escaping or awaiting aid.

For a PDW to be available immediately when required, but
out of the way at all other times, it is important that it should be compact
enough to be carried attached to a soldier's webbing or harness, if not in a
holster, and light enough for it not to become a burden (these will be carried
day in, day out, but rarely used). Compactness is also a major virtue when
stowing the gun in vehicles or aircraft, and when deploying it from vehicle
hatches.

In the interests of reduced
weight and controllability, a PDW should use a less powerful cartridge than the
military rifle/MG round; it therefore makes sense for it to share ammunition
with the service pistol.

A PDW is best fitted with a
compact, zero magnification, holographic, red dot optical sight.

All of this suggests one
of the pistol-calibre PDWs listed above, or something very like them.
The bullpup designs have the advantage of being immediately available
to fire without having to unfold anything (they are also more
comfortable to aim and shoot), but the disadvantage in this role of
being appreciably bigger. A folding-stock gun with the magazine in the
handgrip is therefore indicated. If there isn't time or space to unfold
the stock, the gun can still be used as a pistol.

Of this type of gun, the HK
MP7 is currently the military market leader in the West, but many are concerned about the
terminal effectiveness of the little 4.6 mm bullet. The optimum choice for them,
at least for the time being, would appear to be the Brugger & Thomet MP9 in 9
x 19. With the Swedish M39/B AP loading the 9 mm is very effective against soft body
armour. If more penetration is required, then a loading like the Russian
composite AP could be used. Alternatively, it could easily and economically be rebarrelled to take
the 6.5 x 25 CBJ round in order to achieve the NATO PDW range and penetration
targets, in which respects it is clearly superior to the 5.7 mm and 4.6 mm rounds. It is
also a bit lighter and more compact than the MP7.

However, that
is just one view: others will have good reasons to reach different conclusions. Far from the future choice of
the optimum PDW clarifying, it seems to be becoming more confused. One thing
does remain clear: there will be a continuing need for a compact but effective
selective fire weapon for a variety of roles, and it is likely to become
increasingly important for this to have the potential to penetrate at least some levels of
body armour.